The technical field of this invention is phototherapy and, in particular, methods and devices employing optical fibers or other flexible light waveguides to deliver radiation to targeted biological sites.
Fiber-optic phototherapy is an increasingly popular modality for the diagnosis and/or treatment of a wide variety of diseases. For example, in surgery, infrared laser radiation is often delivered to a surgical site by an optically transmissive fiber in order to coagulate blood vessels or cauterize tissue. Similar fiber-optic delivery systems have been proposed for endoscopic or catheter-based instruments to deliver therapeutic radiation to a body lumen or cavity. U.S. Pat. No. 4,878,492 to Sinofsky teaches the use of infrared light to illuminate the endothelial lining of a blood vessel during balloon angioplasty. U.S. Pat. No. 5,053,033 to Clarke teaches the use of ultraviolet light to prevent the proliferation of smooth muscle cells at an angioplasty site.
Fiber-optic irradiation has also been used to activate remote chemical agents with a patient's body. It is well known that light can promote photochemical reactions which, in the absence of light, would proceed either very slowly or not at all. The use of light to activate chemical agents within a patient is often referred to as "photodynamic therapy." For example, U.S. Pat. No. 4,336,809 (Clark) and U.S. Reissue Pat. No. RE 34,544 (Spears) disclose that hematoporphyrin dyes and the like selectively accumulate in tumorous tissue and that cancerous tissue that has taken up the dye can be preferentially destroyed by radiation (typically high intensity red light) absorbed by the dye molecules during phototherapy.
It has also been desirable to promote photothermal treatment for a variety of diseases. This involves the delivery of optical energy to the desired site and the conversion of that optical energy into thermal energy. The intense heat thus generated can cause undesired tissue to undergo necrosis or to separate from a substrate layer. In addition, high energy, rapidly pulsed laser radiation has also been proposed for essentially non-thermal ablation of tissue.
Typically, light can be delivered to the site of the desired phototherapeutic reaction by inserting a fiber-optic cable into a patient and maneuvering it to the site of the desired photochemical reaction. The position of the fiber's tip can be monitored by including a metallic structure at the tip and monitoring the position of the metallic structure, either visually or by x-ray fluoroscopy. Additionally, metallic structures are sometimes used to reflect light and to thereby control the illumination field within the patient.
When illuminated by light, these metallic structures absorb a small, yet significant amount of optical energy and reradiate it as heat. Since the metallic structures of phototherapeutic instruments are generally in contact with or proximate to surrounding tissue, the rise in temperature of these structures can inflict heat-induced tissue damage on surrounding tissue or melt catheters in the vicinity of the fiber's tip.
Accordingly, there exists a need for better methods and apparatuses for preventing the metallic structure in phototherapeutic devices from being heated excessively by incident light during use.